As this sort of light projection device, as disclosed in Patent Literature 1, there is one configured to be arranged between a workpiece and an imaging device for imaging the workpiece and project light from a light emitting surface facing the workpiece.
More specifically, this one includes a light emitting plate having the light emitting surface, and is configured such that, by forming a plurality of slits in the light emitting plate, the imaging device can image the surface of the workpiece from different directions through the slits.
However, in the above-described configuration, the plurality of slits are formed in the light emitting plate, and therefore as compared with a configuration adapted to form a single slit, the area of the light emitting surface is decreased to reduce the light amount of light to be projected to the workpiece, causing the problems of reducing inspection accuracy and inspection speed.